> movements in the actual prediction market itself, well before the event occurs/market resolves can themselves convey information, about what apparent insiders think (or whales want to manipulate the market to think)

Yes, and surely you see that the inability to distinguish between true signal and deliberate countersignal until after the bet has resolved is an indictment of the very model of predictions markets. Like a qubit, you must collapse the waveform to extract the information.

If you can see which account placed key trades, you can determine if it's likely to be signal/countersignal/neither.

Certainly the platform itself can.